Cool'n'quiet reduce frequency and voltage of the processor when it is NOT IN USE. Although the CPU itself throttles back over certain temperature regardless of Cool'n'quiet. AND it does not affect performance at all.

Cool'n'quiet cause problem when you run out of spec, i.e. overclocking or undervolting.
Basically Cool'n'quiet is an automated version of Clockgen which push the multiplier and voltage down according to system load.

You really need to decide what you are going to use the hsf and fan for.
If you have a look at the overclockers forums, then all the ones ive mentioned come up.
Value buy is arctic freezer64
Performance on a budget is the evo, its not that loud at 200 revs, but you could spend another £12 and replace the fan for a silenx. I might do that. You could even attach two fans.

You can see the reviews in cutompc

But if you add the price of those two together, then maybe the thremaltake big typhoon gives you the best of both worlds. Im thinking of this as well.

The one that looks cool, everyone has been waiting fr is the zalman. rveiews that ive seen are inconclusive. Its quiet though.

i use an arctic cooler 64 (tc) version it's pretty quiet, cheap & definately better than the stock 1. it isn't too heavy, as cheap as chips (bout a tenner on ebay) but is quite large (i had to bend a capacitor a bit on my k8tneo) overall i'm very happy with it.

do a dummy run first on mounting (tip from rave) mine's a mobile athlon 2800+ skt 754 (don't ask it's a weird chip!) but it doesn't have a heat spreader so i cut the 4 little plastic "bumps" off & that did the trick with a perfect cpu shape in the goop. oh, & don't buy from blackcat 2 his products work & arrive quite quick but look at his P&P!!

Went for Arctic Freezer 64 which I got from www.msquared.co.uk and it was straightforward to fit and not as big as I expected. The fan blows air straight through to rear fans and even after install (arctic silver 5 paste) temps idle are 3 degs C and load 7 degs C lower

I expect temps to get lower still as paste 'beds in' !

Thanks for replies peeps

BTWwww.msquared.co.uk is great to deal with and can even 'phone' them and they matched price found in cpucity with no hassle - recommended!!